This invention relates to exterior finishes on buildings, utilizing lath as part of the exterior finish system and, more particularly, to an impervious device used in construction of those exterior finish systems that establishes drainage and air circulation pathways which effectively mitigate wet conditions, which often lead to mold growth.
Stucco and thin veneer brick or stone are popular exterior finish systems. Such wall assemblies often include inner and outer walls. The inner structural wall is typically constructed from concrete masonry units (CMU), wood or steel studs with an interior surface of drywall or the like. The outer face of CMU inner walls typically includes a flashed air and moisture barrier layer which manages air and moisture movement over the face of the inner wall. The outer face of a wood or steel framed inner wall typically includes a layer of sheathing such as plywood, particle board or the like, that is fastened to the framing. Commonly, an air and moisture barrier covers the sheathing material which manages air and moisture movement over the face of that inner wall. The outer wall over both CMU and wood or steel framed inner walls is generally constructed of a cement or modified-cement base layer of the exterior finish system which is applied over a metal or fiberglass flat or self-furring lath. These lath products are permeable and do not stop inbound water movement. During construction of the cement or modified-cement base coat layer in non-cavity wall assemblies, the base coat material will come into permanent contact with the inner wall. This contact is known as bridging and is a permanent viaduct for transporting water from the outer wall to the inner wall.
One potentially catastrophic result of bridging between the inner and outer walls is trapped moisture in that layer of the wall assembly by interfering with the free flow of water which in turn and over time reduces or negates the beneficial physical properties of the air and moisture protection. Furthermore, wetting can saturate insulations which negate their thermal properties.
Benefits of cavity wall construction are known to the building industry. With a minimum ⅜-inch clearance between the inner and outer walls, cavities provide reliable pathways for drainage and air circulation, both characteristics being beneficial for dry and healthy wall assemblies.
Currently there is commercially available netting and fabric cavity protection devices that claim to establish drainage and ventilation spaces, as located between the inner and outer wall components. Although theses nettings and fabrics may perform to a degree of their claim, they aren't as efficient and predictable as a dedicated and defined ⅜-inch deep pathway, which dimension is defined by building sciences as a minimum depth requirement for a cavity.
Furthermore, nettings and fabrics do not offer enough deflective structural support to the exterior finish. To the contrary, they are so weak as to be a detriment to exterior finish performance when exposed to the stresses of repetitive wind and impact related deflection.
Furthermore, netting and fabric cavity protection devices are permeable and allow rates of bulk and vapor transmission to move from being stored in, or leaking through the outer wall to the inner wall.